Multilayer hollow-fiber body and method of making

ABSTRACT

A multilayer hollow fiber body useful, for example, in a blood oxygenator. The multilayer hollow fiber body comprises a single hollow fiber mat arranged in the form of a body comprising a plurality of hollow fiber plies. The mat comprises a plurality of generally parallel hollow fibers disposed at regular intervals, and a plurality of connecting fibers holding the connecting fibers. The mat is repeatedly folded over on itself along fold lines, each of which is at an oblique angle to the hollow fibers, to form a multilayer hollow fiber body in which the hollow fibers of any ply of the multilayer hollow fiber body are disposed so as to cross the hollow fibers of an adjacent successive ply of the multilayer hollow fiber body. Also disclosed is a method of making the multilayer hollow fiber body.

This is a continuation of application Ser. No. 08/565,439 filed Nov. 30,1995, now abandoned.

This invention relates to a multilayer hollow fiber body and method ofmaking such a body, and more particularly to such a hollow fiber bodythat is useful in blood oxygenators and other medical equipment.

BACKGROUND OF THE INVENTION

In the field of membrane blood oxygenators employing a multiplicity ofporous hollow fibers, it has long been recognized that gas transferbetween the lumens of the hollow fibers and the blood circulatingoutside the fibers is optimized when the fibers of adjacent layers crossone another. For example, U.S. Pat. No. 3,794,468 (Leonard) discloseswinding a single porous hollow fiber around a core in such a way thatthe hollow fiber along one layer is generally parallel to itself butdisposed at an angle to the hollow fiber of the immediately adjacentlayers. This provides flow channels for fluid on the outside of thehollow fibers having low resistance and desirable flow characteristicswithout the use of spacers between the layers, which would undesirablyincrease the prime volume of the resulting product and surface area thatblood contacts.

U.S. Pat. Nos. 4,940,617 and 5,143,312 (Baurmeister '617 and '312)disclose forming a structure comprising two superimposed hollow fibermats that are then spirally wound to form a multilayer hollow fiberbody. Each mat comprises a plurality of generally parallel hollow fibersthat are held by solid transverse fibers. The hollow fibers of the twosuperimposed mats are disposed at an equal but opposite angle (otherthan perpendicular) to the longitudinal direction of the mat. The resultis that the hollow fibers of adjacent layers cross one another to formflow channels without the use of spacers. While the concept of employinga mat has certain manufacturing advantages, one problem with theBaurmeister method and product is that it requires the use of two fibermats in order to accomplish the result of crossing the hollow fibers ofadjacent layers. The mats disclosed in the Baurmeister patents areavailable from Akzo Nobel Faser AG, Wuppertal, Germany.

An additional restriction or limitation of the prior systems discussedabove is that they require the hollow fiber structure to extendcompletely around a core or otherwise form an unbroken wound structure.

SUMMARY OF THE INVENTION

This invention provides a multilayer hollow fiber body and a method ofmaking such a body with a single hollow fiber mat, rather than twosuperimposed hollow fiber mats or a structure wound from a single fiber,in which the hollow fibers of adjacent plies or layers of the body crossone another at a desired angle. The resulting hollow fiber body may beformed in many different configurations and used in many differentproducts, particularly including an integral blood oxygenator, heatexchanger and filter, in which the hollow fiber body is wrapped around aheat exchanger manifold, with a gap being formed between edges of thehollow fiber body to receive a blood filter. The hollow fiber body mayalso be kept in a generally flat configuration, or wrapped completelyaround a core with opposite edges of the body engaging one another. Thedifferent configurations that the hollow fiber body may take relative tothe prior systems discussed in the background reduces limitations andrestrictions on the design of products employing such hollow fiberbodies, such as blood oxygenators, blood heat exchangers, dialyzers andother products, in comparison to those prior systems. The hollow fiberbody is designed to promote mixing of blood flow around the hollowfibers without excessive pressure drop.

Generally, a multilayer hollow fiber body of the invention comprises asingle hollow fiber mat arranged in the form of a body comprising aplurality of hollow fiber plies. The mat comprises a plurality of hollowfibers disposed at regular intervals and a plurality of connectingfibers holding the hollow fibers. The mat is repeatedly folded over onitself along fold lines, each of which is at an oblique angle to thehollow fibers, to form a multilayer hollow fiber body in which thehollow fibers of any ply of the multilayer hollow fiber body aredisposed so as to cross the hollow fibers of an adjacent successive plyof the multilayer hollow fiber body.

Preferably, the fold lines are generally parallel to one another, andthe oblique angle between the hollow fibers and the fold lines isbetween approximately 1-15 degrees. Most preferably, the mat isgenerally elongate, the hollow fibers extend at an oblique angle (e.g.,75-89 degrees) with respect to the direction of elongation of the mat,and the fold lines are generally perpendicular to the direction ofelongation of the mat.

Also, preferably, the connecting fibers are disposed at regularintervals, extend generally in the direction of elongation of the mat,and are interweaved with the hollow fibers to hold the fibers in themat.

Most preferably, the distance between the fold lines along any ply isthe same as the distance between the fold lines along any other ply.Alternatively, the distance between the fold lines along any ply mayprogressively increase in an "outer" direction.

In the method of the invention, a multilayer hollow fiber body is madeaccording to the following steps:

(A) interweaving hollow fibers and connecting fibers to form a mat, withthe hollow fibers being generally parallel to one another; and

(B) repeatedly folding the mat over on itself along fold lines that areat an oblique angle to the hollow fibers to form a multilayer hollowfiber body in which the hollow fibers of any ply of the multilayerhollow fiber body are disposed so as to cross the follow fibers of anadjacent successive ply of the multilayer hollow fiber body.

The mat is preferably folded along generally parallel fold lines thatare generally perpendicular to the direction of elongation of the mat,and equally spaced apart so that any ply of the mat has a length betweenfold lines that is generally equal to the length of the other plies

Other features will be pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be further described with reference to the drawingwherein corresponding reference characters indicate corresponding partsthroughout the several views of the drawing, and wherein:

FIG. 1 is perspective view of an elongate, continuous mat of hollowfiber material, illustrating a preferred oblique angle of the hollowfibers relative to the longitudinal axis of the mat;

FIG. 2 is a perspective view of the mat of FIG. 1 being folded alongfold lines that are substantially perpendicular to the longitudinal axisof the mat;

FIG. 3 is side view of the mat of FIGS. 1 and 2 being folded along foldlines resulting in successive layers have successively decreasinglength;

FIG. 4 is a side view of a multilayer hollow fiber body formed by themat folded as illustrated in FIG. 3;

FIG. 5 is an end view of some of the interior components of a novelblood oxygenator and heat exchanger, including the multilayer hollowfiber body of FIG. 4 formed into a generally "C" shaped body;

FIG. 6 is a side view of a multilayer hollow fiber body formed into agenerally "C" shaped body where each successive layer of the mat has thesame length as the other layers;

FIG. 7A is a side schematic view of a generally "C" shaped multilayerhollow fiber body formed over a cylinder, illustrating an angle θ formedbetween the edges of the multilayer hollow fiber body of FIG. 6;

FIG. 7B is a side schematic view of a generally "C" shaped multilayerhollow fiber body formed over a cylinder, illustrating a generallyconstant gap "G" between the edges of a multilayer hollow fiber bodyfolded as illustrated in FIGS. 3-5;

FIG. 7C is a side schematic view of a generally "C" shaped multilayerhollow fiber body formed over a core having an oblong cross section,illustrating a dimension "H" and an angle θ used in calculating thedesired width of each successive layer of the mat;

FIG. 7D is an enlarged side view of a small section of the mat of FIGS.1-7C, illustrating the outer diameter "d" of a hollow fiber and a lumenof the hollow fiber and the weaving of a connecting fiber between thehollow fibers;

FIG. 8 is schematic vertical cross-sectional view of an apparatus forforming a multilayer hollow fiber body from the elongate mat of FIG. 1;

FIG. 9 is top plan view a second embodiment of an apparatus for forminga multilayer hollow fiber body from the elongate mat of FIG. 1;

FIG. 10 is a side elevational view of the apparatus of FIG. 9;

FIG. 11 is a front elevational view of the apparatus of FIGS. 9 and 10;

FIGS. 12A and 12B are corresponding top plan and side elevational viewsof the apparatus of FIGS. 9-11 at a first step of folding a mat with theapparatus;

FIGS. 13A and 13B are corresponding top plan and side elevational viewsof the apparatus of FIGS. 9-12B at a second step of folding a mat withthe apparatus;

FIGS. 14A and 14B are corresponding top plan and side elevational viewsof the apparatus of FIGS. 9-13B at a third step of folding a mat withthe apparatus;

FIGS. 15A and 15B are corresponding top plan and side elevational viewsof the apparatus of FIGS. 9-14B at a fourth step of folding a mat withthe apparatus;

FIGS. 16A and 16B are corresponding top plan and side elevational viewsof the apparatus of FIGS. 9-15B at a fifth step of folding a mat withthe apparatus;

FIGS. 17A and 17B are corresponding top plan and side elevational viewsof the apparatus of FIGS. 9-16B at a sixth step of folding a mat withthe apparatus;

FIG. 18 is a flow diagram of a process of folding a mat with theapparatus of FIGS. 9-17B; and

FIG. 19 is a cross sectional view of an integral blood oxygenator, heatexchanger and filter incorporating a multilayer hollow fiber body of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Now referring to the drawing, an elongate, generally continuous mat ofthe invention is designated by the reference numeral 20. The mats 20 maybe of the type conventionally used in blood oxygenators, and areavailable under the trade designation "OXYPHAN™" membranes from theFibers Division of Akzo Nobel Faser AG, Wuppertal, Germany, or under thetrade designation "CELGARD™ hollow fiber array" from the SeparationsProducts Division of Hoechst Celanese Corporation, Charlotte, N.C. Thesemats 20 are conventionally formed of polypropylene.

The mat 20 includes a multiplicity of conventional microporous hollowfibers 22, and conventional connecting fibers 24 (FIG. 7D) holding thehollow fibers 22. The hollow fibers 22 and connecting fibers 24 arepreferably interweaved so that the connecting fibers 24 hold the hollowfibers 22 in an array. The connecting fibers 24 are preferably solid,rather than hollow. Each hollow fiber 22 comprises a lumen 26 and a wall28 defining the lumen 26. The wall 28 is generally microporous to allowtransfer of gas but not liquid through the wall 28 so that oxygen maypass outwardly from the lumen 26 through the wall 28 into bloodcirculating outside the hollow fiber 22 and so that carbon dioxide maypass inwardly from the blood through the wall 28 into the lumen 26 sothat it may be carried away. According to one example of the invention,approximately thirty hollow fibers 22 are provided per inch (12 fibersper centimeter), and each hollow fiber 22 has an outer diameter ofapproximately 300 micrometers.

The hollow fibers 22 are disposed at regular intervals, and theconnecting fibers 24 are preferably disposed at regular intervals. Asused herein, the term "regular intervals" does not require equalintervals, although equal intervals are preferred. Rather, the term"regular intervals" means, for example, that the hollow fibers 22 aregenerally parallel to one another in the mat 20 before the mat 20 isfolded. As will be discussed below, after the mat 20 is folded, thehollow fibers 22 of one ply will be parallel to one another but willcross the hollow fibers 22 of adjacent plies.

As used herein, the terms "longitudinal", "longitudinally" or "directionof elongation of the mat" refer to the elongate or continuous directionof the mat 20, and the terms "lateral" or "laterally" refer to thedirection across the width of the mat 20, which is perpendicular to thelongitudinal direction of the mat 20. The term "length" in connectionwith the mat 20 refers to a distance in the longitudinal direction ofthe mat 20. The term "width" of the mat 20 refers to the distancelaterally across the mat 20. As used herein, the terms "elongate" or"direction of elongation" do not imply or require the mat to bestretched; they simply refer to the longer dimension of the mat.

The connecting fibers 24 extend generally in the longitudinal directionof the mat 20, and the hollow fibers 22 extend at an oblique angle arelative to the lateral direction of the mat. As used herein, the term"oblique angle" refers to an angle other than zero, 90, 180, 270 or 360degrees. The oblique angle σ is preferably 1-15 degrees (e.g., 5degrees). The hollow fibers 22 can also be considered as extending at anoblique angle relative to the longitudinal direction of the mat 20,which is equal to ninety minus the oblique angle σ. Thus, the hollowfibers 22 preferably extend at an oblique angle of approximately 75-89degrees (e.g., 85 degrees) relative to the longitudinal direction of themat 20. The oblique angle can be formed in the original production ofthe mat 20, or by flexing or displacing one edge of the mat 20longitudinally relative to the opposite edge of the mat 20.

Most preferably, the mat 20 is provided in roll-form with the hollowfibers 22 pre-skewed at the desired oblique angle. Alternatively, themat 20 could be provided with the hollow fibers 22 arranged generallyperpendicularly to the longitudinal direction of the mat 20, and thefirst ply of the mat 20 could be held in a folding apparatus with thehollow fibers 22 skewed at the desired oblique angle, or the mat 20could be processed between the mat-supply roll and the folding apparatusto orient the hollow fibers 22 at the desired oblique angle.

As illustrated in FIGS. 2 and 3, the mat 20 is repeatedly folded over onitself along fold lines, e.g., FL-1, FL-2, . . . , FL-22, FL-N, that aredisposed at an oblique angle relative to the hollow fibers 22. "N", forexample, could equal approximately 50 fold lines. The repeatedly foldedmat 20 forms a multilayer hollow fiber body 30 in which the hollowfibers 22 of any ply, e.g., 31, of the body 30 are disposed so as tocross the hollow fibers 22 of an adjacent successive ply, e.g., 33, ofthe body 30. Preferably, the fold lines FL-1, FL-2 are generallyparallel to one another, and extend generally laterally across the mat20 so that they are at the oblique angle σ relative to the hollow fibers22. The result is that the hollow fibers 22 of one ply cross over theprevious ply at an oblique angle 2σ. Opposite edges 34 and 36 of thebody 30 are defined by the fold lines FL-1, FL-2, . . . , FL-N, of themat 20. Most preferably, the mat 20 is not crimped along the fold lines,FL-1, FL-2, . . . , FL-N, so that gas may flow through any hollow fibers22 that extend past the fold lines.

FIGS. 3 and 4 illustrate one preferred embodiment of the invention, inwhich the plies are laid down in successively decreasing lengths,forming a trapezoid-like shape when viewed from the side. When theresulting body 30 of this embodiment is wrapped around a manifold 32,the ends 34 and 36 of the body 30 may be separated by a constant widthgap "G", as illustrated in FIG. 5. FIGS. 7A, 7B and 7C illustratevarious geometrical aspects to control the configuration of the gap,which are used to specify the length of each of the plies that form themat.

FIG. 7A illustrates geometrical aspects of designing the multilayerhollow fiber body, here 30A, to have a gap that increases by a constantangle θ concentric with the axis of a generally cylindrical manifold 32Aaround which the body 30A is wrapped. The body 30A may be considered ashaving an arcuate or generally C-shaped configuration when viewed fromthe side as in FIG. 7A. The distance along any ply between the foldlines defining that ply may be determined by the following equation:

    Ln=Ln=π(D+2(n-1)d+d)(1-θ/360)

Where:

n=Number of ply starting with 1 at inner ply;

Ln=Distance between fold lines of ply n;

D=Outer diameter of manifold;

d=Outer diameter of hollow fiber illustrated in FIG. 7D; and

θ=Gap angle θ illustrated in FIG. 7A.

FIG. 7B illustrates geometrical aspects of designing the multilayerhollow fiber body, here 30B, to have a constant width or uniform gap Gwhen wrapped around a generally cylindrical manifold 32B. The oppositeedges 34B, 36B of the body 30B of this embodiment either engage oneanother or are separated by a constant width gap G. The distance Lnalong a ply between fold lines is substantially determined by thefollowing equation:

    Ln=π(D+2(n-1)d+d)-G

Where:

n=Number of ply starting with 1 at inner ply;

Ln=Distance between fold lines of ply n;

D=Outer diameter of manifold;

d=Outer diameter of hollow fiber; and

G=Desired uniform gap between the opposite edges of the mat, which maybe zero if the opposite edges engage one another.

FIG. 7C illustrates geometrical aspects of designing a multilayer hollowfiber body, here 30C, wrapped around a manifold 32C having a generallyoblong cross-sectional configuration in such a manner that the oppositeedges 34C and 36C of the body 30C define a gap with edges perpendicularto the linear edges 38 of the cross section adjoining the semi-circles40. The body 30C may be considered as having a generally arcuate "U"shape when viewed from the side as in FIG. 7C. The distance Ln along aply between fold lines is substantially determined by the followingequation: ##EQU1## Where: n=Number of ply starting with 1 at inner ply;

Ln=Distance between fold lines of ply n;

D=Outer diameter of semi-circles of manifold;

d=Outer diameter of hollow fiber;

h=Distance between semi-circles along linear edge; and

θ=Angle forming the arc of ply length at one edge centered on thesemicircle with the gap.

According to the most preferred embodiment of the invention, however,the distance between the fold lines FL-1, FL-2, etc., along any ply isthe same as the distance between the fold lines along any other ply. Asillustrated in FIG. 6, when the multilayer hollow fiber body, here 30D,is wrapped over an oblong manifold 32D, the "inner" plies extend fartheraround the manifold 32D than do the "outer" plies. This is also true ifthe manifold is generally cylindrical as well as other configurations.As used herein, the term "inner ply" refers to the ply closest to themanifold 32A, and the term "outer ply" refers to the ply farthest fromthe manifold 32A. This feature provides certain advantages when employedin the integral blood oxygenator, heat exchanger and filter described ina co-assigned U.S. patent application filed on the same day as thisapplication by Ronald J. Leonard, Attorney Docket No. 50999 U.S.A. 9A,Express Mail Label No. EH086388681US, dated Nov. 30, 1995, titled "BloodOxygenator and Heat Exchanger", which is hereby incorporated herein byreference. For example, since the outer plies do not extend as fararound the unit as do the inner plies, they open up a space between thehollow fiber body and the blood filter that can facilitate venting ofgas upstream of the blood filter or use of a bypass port to bypass thefilter.

FIG. 19 is a cross sectional view illustrating various features of oneof the embodiments of the integral blood oxygenator, heat exchanger andfilter described in more detail in the co-assigned patent application.That apparatus 50 generally comprises a generally cylindrical stainlesssteel heat exchanger barrier 52, generally oblong flexible plastic inletmanifold 54, multilayer hollow fiber body 56 according to thisinvention, integral pleated blood filter 58 received in the gap betweenthe opposite ends of the multilayer hollow fiber body 56, and generallyoblong outer housing 60 receiving the barrier 52, manifold 54, body 56and filter 58. In the apparatus 50, the hollow fibers of the multilayerhollow fiber body 56 extend generally but not precisely parallel withthe axis of the heat exchanger barrier 52 and the slot-like exit opening62 of the inlet manifold 54 so that the blood flow path is almostperpendicular, e.g., 85-89 degrees, to the hollow fibers.

The multilayer hollow fiber body 30 may be formed by manually performingthe step of repeatedly folding the mat 20 along the fold lines, FL-1,FL-2, etc., and this manual process has successfully been employed tomake prototypes of the body 30. A thin board (not shown) may be used tohold down the previous ply or plies while the next ply is being foldedover onto the previous ply.

Most preferably, however, the folding process would be mechanized orautomated. For example, the process could be performed using theapparatus 100 illustrated in FIG. 8. The apparatus 100 comprises aplurality of pins 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122,124, 126, 128, 130, 132, 134, 136, 138, etc., slidably received in aplurality of parallel slots 140 in opposite side walls of a frame 141,and a roller 142 for receiving a mat 144 in roll form. It iscontemplated that a brake or other mechanism would be operativelyconnected to the roller 142 to control feeding of the mat 144 into theapparatus 100.

The pins 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124,126, 128, 130, 132, 134, 136, 138, etc., would initially be positionedat opposite ends of adjacent slots 140 in alternating fashion, and themat 144 would be feed into the apparatus 100. The free end of the mat144 would be held, and the pins would successively be brought acrosstheir respective slots 140, thus folding the mat 144 across a pluralityof fold lines defined by the pins 102, 104, 106, 108, 110, 112, 114,116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, etc. Pins102, 104, 106, 108 and 110 are shown in FIG. 8 as having their rangewithin their respective slots 140 limited by a control mechanism, suchas a computer controlled mechanism, in order to obtain the generallytrapezoid-like shape shown in FIG. 4. The pins 102, 104, 106, 108 and110 could have been allowed to travel the entire distance of theirrespective slots 140 to form the mat 30D illustrated in FIG. 6.Alternatively, the slots 140 could be provided with successivelydecreasing length but that would limit the ability to program differentconfigurations for the multilayer bodies produced by the apparatus 100.

FIGS. 9-18 illustrate an alternative preferred apparatus 200 and methodfor producing a multilayer hollow fiber body according to the invention.This apparatus 200 could either be manually operated or computer/machinecontrolled. The apparatus 200 generally comprises two retractable pins202 and 204, each mounted on a separate frame rotor 206 and 208,respectively, arranged along opposite sides of a vacuum table 210. Rotor206 may also be referred to as "rotor A", and rotor 208 may also bereferred to as "rotor B" Each rotor 206 and 208 is mounted on the table210 for rotation relative to the table 210 to pivot the retractable pins202 and 204 over the surface of the table 210. FIGS. 9-11 illustrate theapparatus 200 as having manually operable handles 212 and 214 mounted onthe rotor 206 and 208, respectively, to facilitate manually moving therotor 206 and 208 and to receive the retracted pins 202 and 204 therein.

FIGS. 12A-17B and 18 illustrate use of the apparatus 200. In FIGS.12A-17B, the figures designated with reference characters ending in an"A" show top plan schematic views of the apparatus 200, and the figuresdesignated with reference characters ending in a "B" show sideelevational schematic views but otherwise show the apparatus 200 at thesame step as the "A" views designated with the same number. FIG. 18 is aflow chart outlining the various process steps used to repeatedly foldthe mat, here designated 216, over itself to form the multilayer hollowfiber body.

The mat 216 is first attached to the vacuum table 210 under pins 202 and204 (step 300), and vacuum is applied to the surface of the table 210 tohelp retain the mat 216 in position (step 302).

As illustrated in FIGS. 12A and 12B, the mat 216 extends down to thetable 210 where it makes a bend as it comes around the second pin 204.The bend around the second pin 204 will constitute a first fold line. Asillustrated in FIGS. 12A and 12B and step 304 of FIG. 18, the first pin202 is moved into its retracted position (step 304), and pin 202 and the"A" rotor 206 are rotated clockwise to position the first pin 202 overto the same side of the table 210 as the second pin 204 is positioned(step 306).

Then, as illustrated in FIGS. 13A-14B, the first pin 202 is moved to itsextended position (step 308), and the first pin 202 and "A" rotor 206are pivoted over the table 210 (step 310), with the first pin 202engaging the mat 216 above the table 210 and second pin 204 to bringanother ply, 218 across the table 210 over the ply 220 held by thesecond pin 204. In step 310, the second pin 204 remains stationaryholding the previously formed ply 220 in position over the table 210.The mat 216 now makes a bend around the first pin 202 adjacent thesurface of the table 210. This bend around the first pin 202 willconstitute a second fold line.

Since the first and second pins 202 and 204 are parallel to one another,the first and second fold lines will also be parallel to one another.The first and second pins 202 and 204 are also perpendicular to thelongitudinal direction of the mat 216 to further define the fold linesas being perpendicular to the longitudinal direction of the mat 216.

Next, as illustrated in FIGS. 15A-B, the second pin 204 is retracted instep 312, and the "B" rotor 208 and second pin 204 are pivotedcounterclockwise in step 314 to position the second pin 204 over to thesame side of the table 210 as the first pin 202 is positioned. Then, thesecond pin 204 is moved to its extended position (step 316; FIGS.16A-B), and the second pin 204 and "B" rotor 208 are pivoted over thetable 210 (step 318; FIGS. 17A-B), with the second pin 204 engaging themat 216 above the table 210 and first pin 202 to bring another ply 222across the table 210 over the ply 218 held by the first pin 202. In step318, the first pin 202 remains stationary holding the previously formedply 218 in position over the table 210 and previous plies, e.g., ply220. The mat 216 now makes a bend around the second pin 204 adjacent thesurface of the table 210. This bend around the first pin 204 willconstitute a third fold line.

Step 320 is a decision step in which a decision must be made as towhether a sufficient number of plies have been formed. Until asufficient number of plies have been formed, the process returns to step304 and repeats steps 304-320. After a sufficient number of plies havebeen formed, the mat 216 is cut from the spool (not shown) to separatethe multilayer hollow fiber body from the roll-form stock of matmaterial (step 322). Vacuum to the vacuum table 210 is turned off instep 324, and the completed multilayer hollow fiber body is removed fromthe apparatus 300 in step 326 so that it may be assembled in the desiredproduct, e.g., a blood oxygenator.

The opposite lateral sides of the hollow fiber body may be embedded inpotting compound as is conventional in the art of forming membrane bloodoxygenators.

The oblique angle σ of the hollow fibers 22 relative to the fold linesFL-1, FL-2, . . . , FL-N is preferably sufficiently great to preventnesting of the hollow fibers 22 of one ply between the hollow fibers 22of either adjacent ply. The specified range of oblique angle σ of 1-15degrees (most preferably 5 degrees) is believed to accomplish thisresult.

The multilayer hollow fiber body of this invention may be employed invarious devices, particularly including integral blood oxygenator, heatexchanger and filter units, as well as other devices. Because the bodyis not formed by continuously wrapping a multiplicity of layers over acore, it is particularly suitable for uses where it is desirable to havea gap between the ends of the body or in which it is desirable to retainthe body in a generally flat configuration. The multilayer hollow fiberbody of this invention provides this flexibility in the design of thedevices into which it is employed.

One advantage of this feature, is that a blood filter 58 (FIG. 19) maybe employed immediately downstream of the hollow fiber body 56 and bloodmay pass directly from the hollow fiber body 56 to the filter 58 withoutintervening collection or distribution manifolds. The blood exits thehollow fiber body 56 in appropriate distributed pattern to pass directlyinto the filter 58.

An additional advantage is that this hollow fiber body may be formedfrom a single mat. There is no need to combine two separate mats intoone structure in order to obtain the proper orientation of the hollowfibers of adjacent layers of the hollow fiber body. There is no need towind a single hollow fiber over a core in a complicated operation.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention as defined in theclaims, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings be interpreted asillustrative and not in a limiting sense.

I claim:
 1. A multilayer hollow fiber body comprising a single hollowfiber mat arranged in the form of a body comprising a plurality ofhollow fiber plies;the mat being elongate and comprising hollow fibersand connecting fibers, the hollow fibers being held by the connectingfibers, the hollow fibers being disposed at regular intervals at anoblique angle relative to the direction of elongation of the mat; andthe mat being repeatedly folded over on itself to form a multilayerhollow fiber body in which the hollow fibers of any ply of themultilayer hollow fiber body are disposed so as to cross the hollowfibers of an adjacent successive ply of the multilayer hollow fiberbody.
 2. A multilayer hollow fiber body according to claim 1 wherein themat is folded over parallel fold lines that are perpendicular to theelongate direction of the mat.
 3. A multilayer hollow fiber bodyaccording to claim 2 wherein the hollow fibers each comprise a lumen anda wall defining the lumen, the wall being microporous allowing transferof gas but not liquid through the wall of the hollow fiber.
 4. Amultilayer hollow fiber body according to claim 3 wherein the obliqueangle between the hollow fibers and the elongate direction of the mat iswithin the range of 85-89 degrees.
 5. A multilayer hollow fiber bodyaccording to claim 4 wherein the distance between the fold lines alongany ply is the same as the distance between the fold lines along anyother ply.
 6. A multilayer hollow fiber body according to claim 1wherein the connecting fibers are:solid disposed at regular intervals;and extend in the elongate direction of the mat.
 7. A multilayer hollowfiber body according to claim 1 wherein the body is formed in an arcuateconfiguration over a manifold.
 8. A multilayer hollow fiber bodyaccording to claim 7 wherein the ply adjacent the manifold constitutesan inner ply and the ply farthest from the manifold constitutes an outerply, the distance between fold lines along a ply being greater thecloser that ply is to the outer ply.
 9. A multilayer hollow fiber bodycomprising a single hollow fiber mat arranged in the form of a bodycomprising a plurality of hollow fiber plies;the mat comprising aplurality of hollow fibers disposed at regular intervals and a pluralityof connecting fibers, the hollow fibers being held by the connectingfibers; and the mat being repeatedly folded over on itself along foldlines, each of which is at an oblique angle to the hollow fibers, toform a multilayer hollow fiber body in which the hollow fibers of anyply of the multilayer hollow fiber body are disposed so as to cross thehollow fibers of an adjacent successive ply of the multilayer hollowfiber body.
 10. A multilayer hollow fiber body according to claim 9wherein the fold lines are parallel to one another.
 11. A multilayerhollow fiber body according to claim 10 wherein the oblique anglebetween the hollow fibers and the fold lines is between approximately1-15 degrees.
 12. A multilayer hollow fiber body according to claim 10wherein the mat is elongate, the hollow fibers extend at an obliqueangle with respect to the elongate direction of the mat, the fold linesbeing perpendicular to the elongate direction of the mat.
 13. Amultilayer hollow fiber body according to claim 12 wherein theconnecting fibers are disposed at regular intervals and extend in theelongate direction of the mat, the connecting fibers being interweavedwith the hollow fibers to hold the fibers in the mat.
 14. A multilayerhollow fiber body according to claim 13 wherein the distance between thefold lines along any ply is the same as the distance between the foldlines along any other ply.
 15. A method of making a multilayer hollowfiber body comprising the following steps:interweaving a plurality ofhollow fibers and a plurality of connecting fibers to form a elongatemat, the hollow fibers being held by the connecting fibers, the hollowfibers being disposed at regular intervals at an oblique angle relativeto the elongate direction of the mat; and repeatedly folding the matover on itself to form a multilayer hollow fiber body in which thehollow fibers of any ply of the multilayer hollow fiber body aredisposed so as to cross the hollow fibers of an adjacent successive plyof the multilayer hollow fiber body.
 16. A method according to claim 15wherein the step of repeatedly folding the mat over on itself furthercomprises folding the mat along parallel fold lines that areperpendicular to the direction of elongation of the mat.
 17. A methodaccording to claim 16 where the step of folding the mat along parallelfold lines that are perpendicular to the elongate direction of the matcomprises folding the mat along parallel fold lines that areperpendicular to the elongate direction of the mat and that are equallyspaced apart so that any ply of the mat has a length between fold linesthat is equal to the length of the other plies.
 18. A method of making amultilayer hollow fiber body comprising the following steps:interweavinghollow fibers and connecting fibers to form a mat, with the hollowfibers being parallel to one another; and repeatedly folding the matover on itself along fold lines that are at an oblique angle to thehollow fibers to form a multilayer hollow fiber body in which the hollowfibers of any ply of the multilayer hollow fiber body are disposed so asto cross the hollow fibers of an adjacent successive ply of themultilayer hollow fiber body.
 19. A method according to claim 18 whereinthe step of repeatedly folding the mat over on itself further comprisesfolding the mat along parallel fold lines that are perpendicular to theelongate direction of the mat.
 20. A method according to claim 19 wherethe step of folding the mat along parallel fold lines that areperpendicular to the elongate direction of the mat comprises folding themat along parallel fold lines that are perpendicular to the elongatedirection of the mat and that are equally spaced apart so that any plyof the mat has a length between fold lines that is equal to the lengthof the other plies.